shetmetal working

1. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
SHEET METALWORKING
1. Cutting Operations
2. Bending Operations
3. Drawing
4. Other Sheet Metal Forming Operations
5. Dies and Presses for Sheet Metal Processes
6. Sheet Metal Operations Not Performed on Presses
7. Bending of Tube Stock

2. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Sheet Metalworking Defined
It includes cutting and forming operations performed
on relatively thin sheets of metal
• Thickness of sheet metal = 0.4 mm (1/64 in) to 6 mm
(1/4 in)
• Thickness of plate stock > 6 mm
• Operations usually performed as cold working

3. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Sheet and Plate Metal Products
• Sheet and plate metal parts for consumer and industrial
products such as
• Automobiles and trucks
• Airplanes
• Railway cars and locomotives
• Farm and construction equipment
• Small and large appliances
• Office furniture
• Computers and office equipment

4. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Advantages of Sheet Metal Parts
• High strength
• Good dimensional accuracy
• Good surface finish
• Relatively low cost
• Economical mass production for large quantities

5. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Sheet Metalworking Terminology
• Punch-and-die - tooling to perform cutting,
bending, and drawing
• Stamping press - machine tool that
performs most sheet metal operations
• Stampings - sheet metal products

6. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Basic Types of Sheet Metal
Processes
1. Cutting
• Shearing to separate large sheets
• Blanking to cut part perimeters out of sheet metal
• Punching to make holes in sheet metal
2. Bending
• Straining sheet around a straight axis
3. Drawing
• Forming of sheet into convex or concave shapes

7. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Figure 20.1 Shearing of sheet metal between two cutting edges: (1) just
before the punch contacts work; (2) punch begins to push into work,
causing plastic deformation;
Sheet Metal Cutting

8. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Figure 20.1 Shearing of sheet metal between two cutting edges: (3)
punch compresses and penetrates into work causing a smooth cut
surface; (4) fracture is initiated at the opposing cutting edges which
separates the sheet.
Sheet Metal Cutting

9. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

10. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Shearing, Blanking, and Punching
Three principal operations in pressworking that cut sheet metal:
• Shearing
• Blanking
• Punching

11. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Shearing
Sheet metal cutting operation along a straight line
between two cutting edges
• Typically used to cut large sheets
Figure 20.3 Shearing operation: (a) side view of the shearing
operation; (b) front view of power shears equipped with inclined
upper cutting blade.

12. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Blanking and Punching
Blanking - sheet metal cutting to separate piece
(called a blank) from surrounding stock in a single
step.
Punching - similar to blanking except cut piece is
scrap, called a slug
Figure 20.4 (a) Blanking and (b) punching.

13. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Clearance in Sheet Metal Cutting
It is the distance between punch cutting edge and die
cutting edge.
• Typical values range between 4% and 8% of stock
thickness
•If too small, fracture lines pass each other, causing
double burnishing and larger force
•If too large, metal is pinched between cutting edges
and excessive burr results

14. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Clearance in Sheet Metal Cutting
• Recommended clearance is calculated by:
c = at
where c = clearance; a = allowance; and t = stock
thickness
• Allowance a is determined according to type of metal

15. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Sheet Metal Groups Allowances
Metal group a
1100S and 5052S aluminum alloys,
all tempers
0.045
2024ST and 6061ST aluminum
alloys; brass, soft cold rolled steel,
soft stainless steel
0.060
Cold rolled steel, half hard; stainless
steel, half hard and full hard
0.075

16. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Punch and Die Sizes
•For a round blank of diameter Db:
•Blanking punch diameter = Db - 2c
•Blanking die diameter = Db
where c = clearance
•For a round hole of diameter Dh:
•Hole punch diameter = Dh
•Hole die diameter = Dh + 2c
where c = clearance

17. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Figure 20.6 Die size
determines blank size
Db; punch size
determines hole size
Dh.; c = clearance
Punch and Die Sizes

18. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Purpose: allows slug or blank to drop through die
• Typical values: 0.25 to 1.5 on each side
Figure 20.7
Angular
clearance.
Angular Clearance

19. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e
Cutting Forces
Estimates of cutting force are Important for determining press size
(tonnage)
F = S t L
where S = shear strength of metal; t = stock thickness, and L = length
of cut edge
L= perimeter length of blank or hole being cut.
If shear strength is unknown, then
F= 0.5 TS t L ( TS = Tensile strength)

20. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

21. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

22. ©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

23. Cutoff and Parting
Cutoff: shearing operation in which blank are separated from the sheet
by cutting the opposite sides of the part in sequence.
With each cut a new part is produced.
Parting: cutting of a sheet-metal by a punch with two cutting edges
that matches the opposite sides of the blank.
©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

24. Cutoff and Parting
©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

25. Slotting, Perforating and Notching
©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

26. Slotting: punching operation that cuts out an elongated or rectangular
hole.
Perforating: simultaneous punching of a pattern of holes in sheet
metal.
Usually for decorative purposes.
Notching: cutting out a portion of metal from the side of the sheet.
©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

27. Trimming, Shaving and Fine blanking
©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e

28. Trimming: cutting operation performed on formed part to remove
excess material.
Shaving: shearing operation performed with very small clearance to
obtain accurate dimensionsand cut edges that are smooth and
straight.
©2007 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 3/e